1. Field of Invention
The invention relates to an illuminating device for a microscope.
In the illuminating beam path, the illuminating device for a microscope contains a lamp, an illuminating optical system and mechanical diaphragms. The size and shape of the diaphragms must be respectively matched to the objective used and to the desired type of illumination. The practice of automatically driving the variable quantities has been adopted for this reason. The mechanical diaphragms and filters in the microscope have therefore being equipped in each case with an electric drive or actuator and with a control device. This type of drive involves a high mechanical and electrical outlay because of the multiplicity of the diaphragms and filters used in connection with the most varied types of microscopic illumination.
2. Description of Related Art
DE 31 08 389 A1 has disclosed an illuminating device for a microscope in which a drivable liquid crystal cell with defined structure is used as a mechanical diaphragm. Differently instructed liquid crystal cells are used in each case for the various types of illumination, such as reflected-light/transmitted-light illumination, oblique illumination, dark-field illumination, phase-contrast illumination and polarization illumination.
Because the electrodes of the respective cell have definitively prescribed structures, they can be used only for prescribed magnification ratios in the microscope. In the event of a change in magnification owing to the use of a different microscope objective, it is necessary to install in the microscope a different liquid crystal cell matched thereto. Moreover, setting various types of illumination requires the various liquid crystal cells to be interchanged with one another. The defined structures mean that the type of illumination can be changed only with a change in hardware.
The drive specified in this document is a computer which is connected to the liquid crystal cell via a special control circuit and through which current can be applied to the prescribed structures of the cell.
A planar light source made from individual LEDs arranged next to one another is disclosed in DE 37 34 691 A1. The LEDs are constructed to be drivable individually and replace the halogen lamp normally used. A disadvantage of this arrangement is that the relatively weakly shining LEDs provide only a limited quantity of light for the microscope illumination. Moreover, such self-illuminating LEDs are relatively large, with the result that only a relatively coarse resolution can be achieved by various diaphragms in the representation.